This invention relates to an apparatus for detecting the volume of blood in a blood reservoir.
An oxygenator circuit for an extracorporeal circulation is often employed for temporarily substituting the function of the heart during an open-heart surgery. A blood reservoir for regulating blood flow is incorporated in such an oxygenator circuit. However, the oxygenator circuit involves dangerous problems such as breakage of an entrance tube to the reservoir and a decrease in blood volume due to increased hemorrhage or urine.
Two types of blood reservoirs have been traditionally used, that is, an open-type reservoir having an upper end open to the atmosphere and a closed-type reservoir in the form of a soft bag. In the open-type blood reservoir, when the blood volume is decreased to zero, air can be sucked into the blood outlet line tube and sent to the patient, which leads to an extremely dangerous situation. In the closed-type blood reservoir, when the blood volume is decreased to zero, air is not sucked as opposed to the open-type blood reservoir, but instead, a negative pressure can be exerted.
There is the need for an apparatus for detecting the volume of blood in a blood reservoir.
In conventional open-type blood reservoirs, various types of detectors for monitoring the fluid level have been employed as blood volume detecting apparatus. Closed-type blood reservoirs, however, are unamenable to such automatic detection as done in the open-type blood reservoirs because no fluid level is formed in the closed-type reservoirs. A side tube may also be affixed to the closed-type blood reservoir in order to provide a visible fluid level. However, air can be sucked through the side tube to impair the advantage of the closed-type blood reservoir.
The blood volume in the closed-type blood reservoir may also be detected by measuring the total weight of the blood reservoir. However, several tubes connected to the blood reservoir render the measurement inaccurate.
The volume of blood in the bag-shaped reservoir may be judged by observinig the contraction of the bag reservoir. In this case, a large-sized detector is required and the measurement becomes inaccurate as the bag is irregularly deformed. The level to be detected is uncontrollable in some cases.